Android led smartphone platforms last month with a 51 percent share of all ad impressions tracked by mobile ad network Millennial Media, according to its Mobile Mix report released today.

That number was down a few percentage points from January but still surpassed the 27 percent grabbed by Apple's iOS. But Apple and iOS took the top spot in other areas.

Among other major players, Research In Motion's BlackBerry OS claimed 17 percent of all impressions, leaving Nokia's Symbian with 2 percent and Microsoft's Windows Mobile with just 1 percent.

Beyond its standard findings, Millennial Media has kicked off a new category for Connected Devices, which looks specifically at tablets and gadgets such as the iPod Touch and certain game consoles rather than smartphones. And in this category, Apple led the pack.

Thanks to the popularity of the iPad, Apple's iOS took home 80 percent of all ad impressions in the new category last month. That compared with Android, which accounted for 17 percent, due largely to the growth of Samsung's Galaxy Tab.

Looking specifically at the device makers, Apple again won the top spot with 28 percent of all ad impressions. Among the 30 mobile devices tracked by Millennial Media, the iPhone took first place with a 16.5 percent share, while the iPod Touch trailed in second place. The iPad found itself sixth on the list.

Ten of the top 30 devices
Millennial Media

How did the newly-launched Verizon iPhone fare in February? Tracking the phone for a total of two weeks last month, Millennial Media found that it scooped up 4.5 percent of all ad impressions among U.S. iPhones, with AT&T accounting for the rest.

Android device makers also did well for the month.

Samsung reclaimed second place over HTC with a 23 percent share of all ad impressions, a 50 percent boost from January. In total, Samsung accounted for seven of the top 30 mobile devices, with its Galaxy Tab tablet and its Fascinate, Forte, and Captivate smartphones hitting the list for the first time.

Dropping to third place, HTC captured slightly more than 11 percent of all ad impressions for the month and also saw seven of its mobile devices on the top 30 list. RIM followed closely in fourth place, with a share of around 11 percent and six of its BlackBerry phones among the top 30 devices.

Among all the devices tracked by Millennial Media, smartphones captured 62 percent of all ad impressions last month, leaving 24 percent for feature phones and 14 percent for other connected devices.